SOHO - Solar and Heliospheric Observatory is a joint project between
the European Space Agency (ESA) and American National Aeronautics and
Space Administration (NASA) EIT - Extreme ultraviolet Imaging Telescope
aboard SOHO which obtains images of the Sun at ultraviolet wavelengths.
The EIT/ SOHO is able to image the solar transition region and inner corona
in several, selected bandpasses in the extreme ultraviolet (EUV).
The best bandpass to coronal holes view is Fe XV 284 A = 2 000 000 K .
Dark regions are coronal holes where the fastest solar wind originates.